In an exemplary power distribution system, a single, relatively high-power supply (hereinafter referred to as a bulk power supply) converts input line voltage to a semi-regulated voltage which is then supplied to a multitude of individual point-of-load power supplies located at the loads to be served. For some applications, power is distributed to the point-of-load power supplies along the back-plane of a modular assembly, and, in such case, the bulk power supply is often referred to as a back-plane power supply. The bulk power supply has its input derived from a prime ac power source which may exhibit substantial voltage transients.
In an electronic system having widely dispersed loads, such as a phased-array radar system or a VLSI system, wherein a single bulk power supply is used, large distribution buses and large energy storage capacitors are required throughout the system in order to maintain voltage regulation. For relatively low load voltages, even larger distribution buses are needed because the power buses must carry higher currents, and even larger energy-storage capacitors are needed.
Although most power distribution systems employ a single bulk power supply to serve the total load, a more recent approach to power distribution involves several bulk power supplies coupled in a parallel relationship so that if one of the bulk power supplies fails, then the other parallel-coupled bulk power supplies provide power to the load. Advantageously, such an arrangement enables the use of smaller distribution buses and energy-storage capacitors because the power supplies are in closer proximity to the respective loads which they serve. Disadvantageously, however, using this approach requires a multitude of dc circuit breakers to protect wiring in the event of a short circuit, and, unfortunately, such dc circuit breakers can be problematic at very high dc bus voltages.